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https://issues.apache.org/jira/browse/HBASE-2468?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12870332#action_12870332
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Andrew Purtell commented on HBASE-2468:
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bq. A single table could be made up of many thousands even hundreds of
thousands of regions? It could be significant. Even if 1000 regions it could
add a huge overhead to instantiating an HTable a user may only use for a single
Get.
Yes but this issue talks about a more likely use case, where someone runs a MR
job over a table and causes a storm of individual Gets to META.
bq. I love these features and have wanted them for a while. Just don't think we
should change default HTable behavior significantly.
Then for the general case that's fine but TIF and TOF should set some flag to
true which causes the prefetch on open to kick in. Reasonable?
> Improvements to prewarm META cache on clients
> ---------------------------------------------
>
> Key: HBASE-2468
> URL: https://issues.apache.org/jira/browse/HBASE-2468
> Project: Hadoop HBase
> Issue Type: Improvement
> Components: client
> Reporter: Todd Lipcon
> Assignee: Mingjie Lai
> Fix For: 0.21.0
>
> Attachments: HBASE-2468-trunk.patch
>
>
> A couple different use cases cause storms of reads to META during startup.
> For example, a large MR job will cause each map task to hit meta since it
> starts with an empty cache.
> A couple possible improvements have been proposed:
> - MR jobs could ship a copy of META for the table in the DistributedCache
> - Clients could prewarm cache by doing a large scan of all the meta for the
> table instead of random reads for each miss
> - Each miss could fetch ahead some number of rows in META
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